Although the present invention can be adapted to clean a windshield or any vehicle window, its greatest advantage is achieved in use on a rear window.
When a motor vehicle operator sees a reduction in visibility through the windshield, he instinctively turns on its cleaning components such as the windshield washer and wiper.
However, an operator is less sensitive to a reduction in visibility through the rear window because his attention and view are primarily directed forward to look out for on-coming traffic.
Therefore, it would be advantageous to be able to rely on a device which would automatically clean the rear windows of vehicles which are so dirty that visibility may be impaired or blocked.
The present invention will achieve this result using the following technique.
Two comparable photosensitive elements are placed on or in the laminated glass of a rear window so that they receive light through the glass. The photosensitive element which receives light directly is much more sensitive to the degree of dirtiness of the glass than the other photosensitive element protected from direct exposure to light and which receives only that portion of the light transmitted by the interior of the glass.
The second photosensitive element serves as reference for measuring the difference in response of the two photosensitive elements. Thus, when the difference in response exceeds a given threshold indicative of the degree of dirtiness incompatible with good visibility, an electronic circuit responsive to this difference actuates the glass cleaning components.
When the necessary cleaning has been performed, the first photosensitive element or measuring element provides a response or indication such that the actuating potential to the electronic circuit is no longer maintained. At this point, the cleaning components are deactivated.
To properly acheive the desired result, the first photosensitive element should be placed in the sweeping field of the wiper.